Evolution of magnetic surfboards and spin glass behavior in (Fe1-pGap)2TiO5

The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe2TiO5has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility (χ) and specific heat data (C) for Fe2TiO5diluted with non-magnetic Ga, (Fe1-pGap)2TiO5, for disorder parameterp= 0, 0.11, and 0.42, and elastic neutron scattering data forp= 0.20. A uniform suppression ofTgis observed upon increasingp, along with a value ofχTgthat increases asTgdecreases, i.e.dχ(Tg)/dTg<0We also observeCT∝T2in the low temperature limit. The observed behavior places (Fe1-pGap)2TiO5in the category of a strongly geometrically frustrated SG.

Synthesis and characterization of bulk Nd1-x Sr x NiO2 and Nd1-x Sr x NiO3

The recent reports of superconductivity in Nd_1-x Sr _x NiO₂/SrTiO₃ heterostructures have reinvigorated interest in potential superconductivity of low-oxidation state nickelates. Synthesis of Ni¹⁺-containing compounds is notoriously difficult. In the current work, a combined sol-gel combustion and high-pressure annealing technique was employed to prepare polycrystalline perovskite Nd_1-x Sr _x NiO₃ (x = 0, 0.1, and 0.2). Metal nitrates and metal acetates were used as starting materials, and the latter were found to be superior to the former in terms of safety and reactivity. The Nd_1-x Sr _x NiO₃ compounds were subsequently reduced to Nd_1-x Sr _x NiO₂ using calcium hydride in a sealed, evacuated quartz tube. To understand the synthesis pathway, the evolution from NdNiO₃ to NdNiO₂ was monitored using in situ synchrotron x-ray diffraction during the reduction process. Electrical transport properties were consistent with an insulator-metal transition occurring between x = 0 and 0.1 for Nd_1-x Sr _x NiO₃. Superconductivity was not observed in our bulk samples of Nd_1-x Sr _x NiO₂. Neutron diffraction experiments at 3 and 300 K were performed on Nd_0.9Sr_0.1NiO₂, in which no magnetic Bragg reflections were observed, and the results of structural Rietveld refinement are provided.